dan springer is live in seattle with more on all of this. dan? >> reporter: jenna, the bottom line the nstb is one month into the investigation into what sparked a fire onboard a 787 that was parked at boston's logan airport and they still don't know the cause. investigators have made some progress as they run a number of the tests on the battery that caught fire. they concluded a short circuit in a single cell of the eight-cell battery cause overheating. thermal run away is not supposed to happen. in this case it spread to the whole batry. the in tsb criticized boeing and the faa for problems in battery certification process. there is lot of talk that the faa trusted boeing engineers too much. boeing concluded thermal run away in a lithium-ion battery would happen once in less than 10 million flight hours. so far the dreamliners have flown less than 100,000 hours and it has happened twice. >> this investigation has demonstrated that a short-circuit in a single cell can propagate to adjacent cells and result in smoke and fire. the assumptions use